U-2R FLIGHT PERFORMANCE DATA ANALYSIS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP68B00724R000200190001-9
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 8
• Document Creation Date: December 16, 2016
• Document Release Date: August 9, 2004
• Sequence Number: 1
• Publication Date: December 31, 1969
• Content Type: MFR

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Copy of 13
31 December 1969
MEMORANDUM FOR THE RECORD
SUBJECT: U-2R Flight Performance Data Analysis
REFS : A - LAC Report No. SP-1125, 28 Nov 1966
"Manufacturer's Model Specification High
Altitude Reconnaissance Airplane"
B - LAC Report No SP-1233, 1 Sept 1967
"Performance, Stability and Control of the
L-351 Airplane"
C - LAC Report No SP-2081, 16 Sept 1968,
"Maximum Power Design Weight Mission
Aircraft S/N 055"
D. LAC Report No SP-2096, 8 Oct 1969
"Aircraft Performance Tests" (U-2R)
E. Pratt & Whitney Aircraft Specification
No N-2614-G, 10 Feb 1958 with Appendix B,
8 Nov 1965, Reissued : 25 May 1967.
Model J75-P-13B Engine
INTRODUCTION
An analysis has been made of all significant flight
data available to date from U-2R aircraft in order to evaluate
the performance of the flight test aircraft relative to the
performance predicted in the Model Specification (Reference A)
and in the more complete performance report LAC Report No SP-1233
"Performance, Stability and Control of the L-351 Airplane"
(Reference B). A secondary purpose of this analysis was an
evaluation of the performance of the actual operational aircraft
relative to the model specification and the flight test aircraft.
An analysis of engine performance relative to the engine
specification and its effect on airplane performance was also
included.
USAF review(s) completed.
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The data analysed herein includes recorded flight data
from the instrumented flight test aircraft (051), recorded
data from an operationally configured aircraft (055) and
pilot recorded fuel curve data from operational aircraft
Serial Numbers 052 through 058 inclusive. Data has been
analysed from a total of approximately 25 maximum altitude
flights and the results are displayed in the attached curve
sheets.
The airplane performance parameters evaluated are altitude
capability and range factor as a function of gross weight and
the engine performance parameters are Engine Pressure Ratio
(EPR) and fuel flow versus altitude. Since aircraft performance
is affected by engine performance and engine performance (EPR)
is proportional to oorrected exhaust gas temperature, which
in a function of exhaust gas temperature and free air
temperature, both of these significant temperatures are plotted
for all flights. Engine EPR is the best indicator of engine
output (thrust) available from cockpit instruments and while
it is more directly a measure of the ability of the gas
generator portion of the engine to develop a high pressure gas
(the stuff from which thrust is made) it does not include the
effects of nozzle/ejector efficiency which also affects final
thrust output. For a given aircraft design i.e., a given
aircraft engine installation, EPR is a direct measure of
thrust capability. The range factor term used here is gross
weight x velocity A fuel flow
CONCLUSIONS
A number of significant conclusions relative to the
performance of the U-2R aircraft and the J75-P--13B engine
can be reached as a result of this data analysis.
A. The performance of flight-test aircraft (051)
duplicates that presented in LAC SP-1233 on both
altitude and range factor for a given gross weight.
The actual altitude of the aircraft for a given gross
weight was somewhat below the aircraft specification
due to the fact that the engine thrust was somewhat
below the engine specification performance. When the
aircraft performance is corrected to that which would
result from specification engine performance, the
aircraft altitude capability for a given gross weight
agrees with the values given in the Specification
Performance Report. (See Figures 1 and 5).
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The Range Factor data for the flight test aircraft
also agrees well with predicted performance when engine
fuel flow is corrected to the values predicted in the
engine specification. (See Figure 5A).
B. Average performance of the operationally
configured aircraft is quite predictable and falls
generally about 1200 to 1300 feet below the predicted
aircraft specification performance on an altitude
versus gross weight basis. This is 200 to 300 feet
below the lower limit of the band of performance
shown in the U--2R-1 Manual. This 1200-1300 ft. altitude
decrement occurs as a result of an average engine thrust
deficiency of 3.5% below specification and an average
operational aircraft drag increment of 5% above the
predicted aircraft performance and the performance of
the flight test aircraft. It is worth noting that this
5% drag penalty of approximately 55 pounds 0 Mn .72
and 70,000 feet is equivalent to the dynamic pressure
(or the drag with a CD of 1.0) on an area of li square
feet at this flight condition. It is indicative of
the penalties which occur from adding proturberances
of any kind externally on the aircraft. (See Figures
2, 2A and 3.) As shown in Figure 3A there is considerable
scatter in values of fuel flow and range factor apparently
due to the accuracy of pilot read cockpit data used to
calculate these values. The average fuel flow and range
factor show good agreement with engine and aircraft
predicted values respectively. A special range calibration
flight #23 was flown with aircraft #055 and these results
are shown in Figures 6 and 6A and described in Reference C.
As shown in Figure 6A, the range factor at all gross
weights exceeds the specification value by an average of
2.1%. The total range at maximum altitude should exceed
the specification value by about this amount.
C. A considerable amount of scatter exists in the
cockpit read engine performance data. The EPR data in
particular after correction to'a standard day temperature
results in values which range from 3.4% below to 1.7%
above the specification value at 70,000 feet. This
range of EPR values results in estimated thrust values
which range from about 5.5% below specification to about
2.8% above specification. Engine fuel flow data while
showing some degree of scatter generally agrees reasonably
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well with the engine specification value. This con-
siderable variation in engine performance will be
reviewed with airframe and engine contractor performance
engineers to ascertain if any significant clues as
to possible causes such as engine internal component
performance or installation effects appear worthy of
further study or investigation.
D. As would be expected, the effects of free air
temperature on engine performance are quite significant.
The very low free air temperatures, which exist at
altitude in areas such as the Far East where altitude
temperature profiles approximate or are colder than a
defined standard tropical day, provide a substantial
increase in high altitude engine thrust and improved
aircraft altitude capability. (See Figures ,4 and 4A).
E. A 1962 Standard day is a better standard than
a 1959 standard day and should be used in all future
high altitude aircraft programs. A 1962 standard day
is a more typical day for flight test operations in
the Edwards Air Force Base area and simplifies all
cg alibrations and corrections. Writing specifications
and predicting performance on a 1959 standard day basis
results in somewhat optimistic performance for altitudes
above 65,000 feet since actual temperatures above this
altitude are generally warmer than a 1959 standard day.
DISCUSSION
This analysis is based on a review of all the significant
flight data available from the U-2R aircraft and includes
recorded data from the instrumented flight test aircraft and
pilot recorded fuel curve data from operational aircraft.
Aircraft and engine performance has been plotted and analysed
from approximately 25 flights. In addition to aircraft and
engine performance and the effect of engine performance on
aircraft performance, the effects of ambient temperature and
exhaust gas temperature levels on engine performance have
been analysed. The correction factors for these various
effects are as follows:
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e 5
-10C F.A.T.
+ .012
EPR
+1?C E.G.T.
+ .003
NPR
1% EPR 1.64% Thrust
1% Thrust 150 ft. of Altitude
NOTE: A 1?C lower free air temperature results
in 4 times the improvement in EPR which
results from a 1?C increase in EGT, due
to the fact that EPIC is proportional to
corrected EGT (EGA'/e2) where 92-Compressor
inlet total temperature divided by standard
day temperature at sea level.
While the pilot recorded fuel curve data exhibits a
considerable amount of scatter compared to accurate recorded
data from the flight test aircraft, significant trends in
performance of the operational aircraft can be determined.
Considerable scatter would be expected in the pilot recorded
data due to the accuracy of cockpit instruments and the
degree of accuracy utilized by various pilots in reading
instruments and recording data as compared to flight recorded
data on the flight test aircraft.
The engine specification EPR performance as shown on
the curves is generally presented on the basis of either a
1959 standard day or a 1962 standard day and both are shown
on most curves. On curves where performance is compared
with specification, a 1959 day is generally used since the
aircraft and engine specifications were based on this standard.
However as stated earlier a 1962 standard day appears to be
more representative of the free air temperature data presented
in the report with the exception of the dta obtained in the
-st. A 1959 standard day is based on a constant temperature
of --56.500 at U-2R cruise climb altitudes where a 1962 standard
day is somewhat warmer than -56.5?C at altitudes above
65,600 ft. with the difference between the two standard days
increasing with altitude. (See Figure 1)
he difference at (a 1962 day being 20C warmer
than 1959 standard day) results in a reduction in EPR of
about 3/4 of 1%, 1.2% reduction in thrust and a reduction in
ititude of 180 feet. In the Far East, temperature data more
nearly approximates a tropical standard day altitude temperature
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profile which results in a significant boost in engine and
aircraft performance at U-2R climb and cruise-climb altitudes
and reduces the time required to reach a given penetration
altitude.
The performance of the flight test aircraft (051) was
reviewed primarily on the basis of a particular test flight
081) whore free air temperatures at altitude generally
approximated a standard day. This data is shown in figures
5 and 5A and is summarized in Figure 1 where a comparison is
also made of 051 performance with predicted values and the
band of performance (altitude versus gross weight) presented
in the U-2R-1 manual. The actual flight data for the test
aircraft is approximately 500 ft. below the predicted altitude.
However, when the thrust deficiency of the engine is accounted
for, the altitude versus gross weight profile matches the
predicted values. The actual performance of the engine
(8/N 612621) installed in this test aircraft on flight #81
is also shown in Figure 1 where a comparison is made with
engine specification EPR values. (C3 4Figure 2 represents an attempt to correct all engine
EPE data at 70,000 it. for variations in exhaust gas
temperature and free air temperature. As can be seen from
this figure there is a considerable amount of scatter in this
corrected SPR data. The points shown on the aircraft (altitude
versus gross weight) performance curve of figure 2 were
obtained by taking the gross weight values from all the air-
craft curves at 70,000 ft. and correcting the altitude to the
altitude capability the aircraft would have with specification
engine performance (i.e. an NPR of 3.26 on a 1962 standard day)
at its actual gross weight at 70,000 ft. A 1959 standard day
ould raise all points about 180 ft. in altitude. This
tion to the altitude versus gross weight data brings
aircraft data fairly well within the band of expected
performance shown in the -1 manual. However, as stated
previously an average operational aircraft with an average
engine would fly 200 to 300 ft. below the manual band.
Figure 2A is probably one of the most significant curves
of this report in so far as it portrays a good summation of
operatio>al aircraft performance. This plot is basically a
lift-drag polar. The points shown are not actual data points
but are based on gross weight and EPR values taken at 70,000
from faired curves through the actual data
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points. The effect of varying engine performance is
accounted for by plotting gross weight versus EPR. This
plot also tends to Indicate that the cockpit read data is
reasonably consistant and accurate and that the rather wide
variation in EPR values among the various engines is real.
Perhaps one should expect considerable variation in engine
performance at these flight conditions since a multi stage
axial flow engine IS aerodynamically much more complicated
than an aircraft at this high altitude lowReynolds number
regime.
Figure 3 shows the uncorrected values of gross weight,
WE, SGT and FAT obtained from faired curves through the
actual data plots at 70,000 feet. This in the data from
which the corrected values of Figure 2 were obtained. Figure
3A presents fuel flow and range factor values at 70,000 ft.
and while the data scatters over a fairly wide range, mean
values are generally close to predicted. The wide degree of
scatter which occurs in this data is apparently due to combined
errors in the data (distance, time, and fuel remaining) from
which fuel flow and range factor are calculated.
Figure 4 shows the very beneficial effect of cold
(standard tropical day) free air tatures at altitude on
engine and aircraft performance. o rtropicalday effects
on engine and aircraft performance on this curve are estimated.
Aircraft 055 was used an a reference here since a more complete
and well documented set of data was available from flight 23
ofLthis aircraft and both the aircraft and engine demonstrated
near average performance on this flight with near standard day
free air temperatures. However, some of the actual data
acquired in the Far East for verification of the final EPR
schedule for engine operation and shown in Figure 4A provided
excellent engine performance. This data was acquired on article
058 with engine serial number 612627 installed. Indications
are that in addition to the beneficial cold temperature effect
this engine also provides considerably better than average
standard day performance. Additional fuel curve data obtained
very recently (16 December 1969) on the same aircraft in the
Far last with engine SIN 612626 installed also indicated
excellent engine performance with EPR values as high as 3.35
at 70,000 feet.
The actual recorded data for flight 81 of aircraft 051
are shown in figures 5 and 5A. Figure 5A displays fuel flow
and range factor data for the engine and airframe respectively.
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The PAT curve (figure 5) indicates that free air temperatures
were somewhat colder than standard and when
this correction is applied to the engine ue ew data an
average curve would fall on the predicted curve. Since Range
Factor equals gross weight x nautical miles per hour pounds
of fuel per hour, correcting the slightly high values of fuel
flow at altitudes down to the engine specifi-
cation curve would bring the aircraft range values up to
their predicted values.
Figures 6 and 6A are uncorrected flight recorded data
from flight 23 of aircraft 055 and are particularly significant
since they represent performance of an average aircraft and
engine at near 1962 standard day conditions.
Figures 7 through 18 inclusive are the actual plots of
uncorrected pilot recorded data from operational aircraft and
generally result in rather well defined curves. The A series
of curves, however, presenting engine fuel flow and aircraft
range factor generally exhibit a rather wide degree of data
scatter due apparently to an accumulation of errors in the
cockpit instrument data from which they were calculated. Some
of the best aircraft and engine performance data shown in
these curves was obtained from flights of aircraft 057 and
058 n _the cold free air temperatures in the area of 'the Par
East operating base. The data from aircraft 058 displayed in
Figures 17 and 17A are a case in point where both the aircraft
and engine performance are considerably above their respective
predicted values due to the very cold free air temperatures
and the fact mentioned previously that this engine (S/N 612627)
provides relatively good performance (i.e. above specification)
even on a standard day.
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